Implants With Roughened Surfaces

ABSTRACT

Provided are methods for processing a green body that includes compacted metal powder, comprising impacting the green body with a particulate material for a time and under conditions effective to displace a portion of the metal powder from the green body. The present methods can be used to prepare green bodies that have “roughened” surfaces and that can be used to make orthopedic implants displaying low movement relative to bone when installed in situ, which corresponds to higher stability upon implantation and decreases the time required for biological fixation of the implant. Also provided are implants comprising a metallic matrix, and methods comprising surgically installing an implant prepared from a “surface roughened” green body in accordance with the present invention.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional ApplicationNo. 61/055,304, filed May 22, 2008, the entire disclosure of which isincorporated herein in its entirety.

FIELD OF THE INVENTION

The present invention relates to orthopedic implants and materials usedfor making orthopedic implants, as well as methods for producing andusing such implants and materials.

BACKGROUND OF THE INVENTION

The “space holder” method is a well known process for making metallicfoam structures and employs dissolvable or otherwise removablespace-holding materials that are combined with metallic powders andsubsequently removed from the combination by various methods, includingheat or liquid dissolution, leaving behind a porous matrix formed fromthe metallic powder. The porous matrix material is then sintered tofurther strengthen the matrix structure. Numerous variations on thespace holder concept are known in the art. See, e.g., U.S. Pat. Nos.3,852,045; 6,849,230; U.S. Pub. Nos. 2005/0249625; 2006/0002810.

Surface roughness is an important attribute of orthopedic implants thatare intended for cementless fixation to bone. High surface roughness cancorrespond to elevated friction against bone and general stability uponinitial implantation, both of which are conducive to long-term stabilityvia bone and tissue ingrowth. Several porous coating products have beendeveloped for use in connection with implant surfaces, including implantcoatings that are said to enhance biological fixation and maximizetissue ingrowth. Such coatings are applied to the face of an implant inorder to impart a rough, high friction surface that interacts with bonein a manner that leads to a decrease in relative movement between theimplant and the bone while providing a network of interconnected poresfor secure fixation of the implant to bone by the ingrowth of bonetissue.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides methods for processing agreen body that includes compacted metal powder comprising impacting thegreen body with a particulate material under conditions effective todisplace a portion of the metal powder from the green body.

Also provided are implants comprising a metallic matrix, wherein atleast one surface of the metallic matrix has a static frictioncoefficient with a polymer bone analog of about 0.7 or higher. Alsodisclosed are implants comprising a metallic matrix, wherein at leastone surface of the metallic matrix has a roughness that corresponds to aPa value of at least about 20, a roughness that corresponds to a Ppvalue of at least about 60, a roughness that corresponds to a Pt valueof at least about 140, or a roughness that corresponds to a Pq value ofat least about 30.

The present methods also include surgically installing an implant madein accordance with the disclosed processing techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic flowchart that illustrates methods in accordancewith one aspect of the present invention.

FIGS. 2A and B show lateral surface profiles of green bodies of whichsections have been processed in accordance with the inventive methods.

FIG. 3 provides measurements of static friction coefficient of variousmaterials against a polymer bone analogue.

FIG. 4 depicts a graph that compares surface roughness of a CP-Timetallic matrix sample with the pressure (psi) at which the green bodysample from which the metallic matrix sample was prepared was impacted(“blasted”) with the particulate material, wherein the surface roughnessis expressed in terms of the Pa parameter.

FIG. 5 depicts a graph that compares surface roughness of a CP-Timetallic matrix sample with the pressure (psi) at which the green bodysample from which the metallic matrix sample was prepared was impacted(“blasted”) with the particulate material, wherein the surface roughnessis expressed in terms of the Pp parameter.

FIG. 6 depicts a graph that compares surface roughness of a CP-Timetallic matrix sample with the pressure (psi) at which the green bodysample from which the metallic matrix sample was prepared was impacted(“blasted”) with the particulate material, wherein the surface roughnessis expressed in terms of the Pt parameter.

FIG. 7 depicts a graph that compares surface roughness of a CP-Timetallic matrix sample with the pressure (psi) at which the green bodysample from which the metallic matrix sample was prepared was impacted(“blasted”) with the particulate material, wherein the surface roughnessis expressed in terms of the Pq parameter.

FIG. 8 depicts a graph that compares surface roughness of a Ti-6Al-4Vmetallic matrix sample with the pressure (psi) at which the green bodysample from which the metallic matrix sample was prepared was impacted(“blasted”) with the particulate material, wherein the surface roughnessis expressed in terms of the Pa parameter.

FIG. 9 depicts a graph that compares surface roughness of a Ti-6Al-4Vmetallic matrix sample with the pressure (psi) at which the green bodysample from which the metallic matrix sample was prepared was impacted(“blasted”) with the particulate material, wherein the surface roughnessis expressed in terms of the Pp parameter.

FIG. 10 depicts a graph that compares surface roughness of a Ti-6Al-4Vmetallic matrix sample with the pressure (psi) at which the green bodysample from which the metallic matrix sample was prepared was impacted(“blasted”) with the particulate material, wherein the surface roughnessis expressed in terms of the Pt parameter.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention may be understood more readily by reference to thefollowing detailed description taken in connection with the accompanyingfigures and examples, which form a part of this disclosure. It is to beunderstood that this invention is not limited to the specific products,methods, conditions or parameters described and/or shown herein, andthat the terminology used herein is for the purpose of describingparticular embodiments by way of example only and is not intended to belimiting of the claimed invention.

In the present disclosure the singular forms “a,” “an,” and “the”include the plural reference, and reference to a particular numericalvalue includes at least that particular value, unless the contextclearly indicates otherwise. Thus, for example, a reference to “amaterial” is a reference to one or more of such materials andequivalents thereof known to those skilled in the art, and so forth.When values are expressed as approximations, by use of the antecedent“about,” it will be understood that the particular value forms anotherembodiment. As used herein, “about X” (where X is a numerical value)refers to ±10% of the recited value, inclusive. For example, the phrase“about 8” refers to a value of 7.2 to 8.8, inclusive; as anotherexample, the phrase “about 8%” refers to a value of 7.2% to 8.8%,inclusive. Where present, all ranges are inclusive and combinable.

The disclosures of each patent, patent application, and publicationcited or described in this document are hereby incorporated herein byreference, in their entirety.

Porous coating products may be applied to one or more of the outersurfaces of shaped implants to increase friction between such implantsand bone while providing a network of interconnected pores for securefixation of the implant to bone by the ingrowth of bone tissue. Roughsurface coatings exhibit peaks that, when present on an implant face,are believed to lead to increased contact pressure and thereby ploughingand abrasive interaction between the implant face and the surface of anadjoining bone. Such phenomena at the surface of the implant increasethe resistance to relative movement between the implant and bone, whichcorresponds to higher stability upon implantation and may increase thelikelihood of achieving biological fixation of the implant.

The present invention represents a companion method or an alternative tothe use of porous coating products on the surface of orthopedic implantscomprising a metallic matrix. It has presently been discovered that thesurface topography of a green body, i.e., an article comprising acompacted but unsintered mass comprising metal powder, may be altered bydisplacing portions of the compacted metal powder from the surface ofthe green body. The resulting topography is characterized at least inpart by pits or valleys and peaks, which, much like a coated surface ofan implant, allows an implant formed from such green body to exhibitincreased friction with an abutting bone surface. The attendant benefitsof such increased friction are evident in view of the precedingdiscussion, and include implant stability and increased likelihood ofbiological fixation through successful integration with bone and tissue.Unlike a coated implant, however, the topography of the resultingimplant is an inherent characteristic of the implant itself and does notderive from the use of a substance other than the implant material.Thus, the presently disclosed approach has the potential to reduce thecost of preparing orthopedic implants, at least because a surfacecoating need not be separately acquired.

In accordance with the present invention there are provided methods forprocessing a green body that includes compacted metal powder, suchmethods comprising impacting the green body with a particulate materialfor a time and under conditions effective to displace a portion of themetal powder from the green body. Also provided are green bodies thatinclude compacted metal powder, the green body having been impacted witha particulate material for a time and under conditions effective todisplace a portion of the metal powder from the green body. The presentmethods may further include sintering the green body following thedisplacement of a portion of the metal powder from the green body. Asintered green body, which may optionally undergo machining or otherprocessing steps following such sintering, can function as an orthopedicimplant that may be installed within a patient. Accordingly, the presentmethods may further comprise surgically installing into a patient animplant made from a green body that has been processed and sintered inaccordance with the present invention.

The green body that is impacted with the particulate material may beprepared using traditional techniques. The preparation of a green bodymay comprise mixing at least one metal powder with an extractablematerial, thereby forming a powder mixture in which the metal powder andthe extractable material assume respective positions, shaping the powdermixture into a shaped object, and compacting the shaped object to formthe green body.

The metal powder may comprise any biocompatible metal, nonlimitingexamples of which include titanium, a titanium alloy, a cobalt-chromiumalloy, molybdenum, tantalum, niobium, zirconium, stainless steel, or anycombination thereof. The extractable material may be a material that issoluble in an aqueous fluid, an organic solvent, or both, and mayinclude a salt, a sugar, a solid hydrocarbon, a urea derivative, apolymer, or any combination thereof. Suitable examples include sodiumchloride, potassium chloride, sucrose, potassium sorbate, carbamide,biuret, ammonium carbonate, ammonium bicarbonate, naphthalene, or anycombination thereof. Alternatively, the extractable material may beremoved under heat and/or pressure conditions; for example, theextractable material may volatilize, melt, or otherwise dissipate as aresult of heating. Examples of such extractable materials includeammonium bicarbonate, urea, biuret, melamine, ammonium carbonate,naphthalene, sodium bicarbonate, and any combination thereof.

Suitable techniques for mixing a metal powder with an extractablematerial will be readily appreciated by those skilled in the art. See,e.g., U.S. Pat. Nos. 3,852,045, 6,849,230; U.S. Pub. Nos. 2005/0249625,2006/0002810. Ideally, the mixing results in a substantially uniformdispersion of the particles comprising the minor component of the powdermixture among the particles comprising the major part of the powdermixture. The metal powder may comprise about 18 to about 67 weightpercent of the powder mixture, the balance of the powder mixturecomprising the extractable material. Once the extractable material isremoved from the green body in later stages of the present methods, theresulting porosity of the green body may be about 50% to about 90%,preferably about 60% to about 85%. The removal of the extractablematerial is described more fully infra.

Following the mixing of the at least one metal powder with theextractable material, the powder mixture may be shaped into a shapedobject. The shaping process can comprise filling a mold with the powdermixture, the mold having at least roughly the three-dimensionalparameters of the desired final implant product, allowing for subsequentprocessing steps such as machining. In other embodiments, the mold neednot be designed to produce near-net shape parts or parts whose moldedform resembles the desired final, sintered part; molds may producegeneric shapes, such as bars, rods, plates, or blocks, that may besubsequently machined in the green state to produce a part that aftersintering-induced shrinkage closely approximates the desired shape ofthe final product, with optional machining of the sintered part. Moldsand mold assemblies for such purposes are well known among those skilledthe art and may allow for the preparation of bodies that are, forexample, spherical, spheroid, ovoid, hemispherical, cuboid, cylindrical,toriod, conical, concave hemispherical (i.e., cup-shaped), irregular, orthat adopt any other desired three-dimensional conformation. Once formedfrom the powder mixture in accordance with the preceding, the resultingshaped object may be compacted to form the green body. The shaped objectis compacted while contained within a mold assembly. Compacting may beuniaxial, multi-axial, or isostatic. In preferred embodiments, a coldisostatic press is used to compact the shaped object into the greenbody. Following the compacting procedure, the resulting green body maybe removed from the mold and processed. Processing may include machiningor otherwise refining the shape of the green body.

Whether or not machining is performed after compacting, the green bodymay then be exposed to a solvent in which the extractable material issoluble. As indicated above, the extractable material may be soluble inan aqueous solvent, an organic solvent, or both. The exposure of thegreen body to the solvent may comprise immersing the green body in thesolvent, for example, by immersing the green body in a bath comprisingthe solvent for a time sufficient to remove at least some of theextractable material. Depending on various factors such as the type ofsolvent chosen relative to the identity of the extractable material, thetemperature of the solvent, and the time of exposure to the solvent, theremoval of extractable material from the green body can range frompartial to complete. The exposure of the green body to the solvent inwhich the extractable material is soluble preferably removes theextractable material from at least the surface of the green body to adepth at least about 1 mm, at least about 3 mm, at least about 5 mm, atleast about 7 mm, or at least about 10 mm from any given surface of thegreen body.

In another embodiment, the extractable material is insoluble in aqueousor organic solvent, and is removable under heating conditions. In suchcircumstances, after the formation of the green body via compacting (andwhether or not machining is performed following compacting) the greenbody may be heated for a time and under conditions effective toevaporate at least some of the extractable material yet substantiallymaintain the metal powder in its position in the green body. Dependingon various factors such as the identity of the extractable material, thetemperature of the heating environment, and the time of heating, theremoval of extractable material from the green body can range frompartial to complete, and the heating of the green body preferablyremoves the extractable material from at least the surface of the greenbody, down to at least about 5% of the total depth of the green body.Preferably, the thermal removal of extractable material is performed attemperatures much lower than sintering temperature, in order to avoidcontamination of the green body material with C, N, or H from organicspace holders. For example, the thermal removal of extractable materialmay occur at less than about 100° C., which is sufficient to cause thedecomposition of some extractable materials, such as ammoniumbicarbonate.

A green body in accordance with the present invention may be impactedwith a particulate material for a time and under conditions effective todisplace a portion of the metal powder from the green body. Thedisplacement of a portion of the metal powder from the green body altersthe surface geometry of the green body. The altered surface geometry maybe described as “roughness” and is generally characterized, at least inpart, by regular or irregular pits (or valleys) and peaks. In accordancewith the present invention, roughness can be varied by numerous factorsincluding the force with which the particulate material impacts thegreen body, the characteristics of the particulate material (includingmaterial type, and particle size and shape), the distance between thesource of the particulate material and the green body, the geometry ofthe orifice from which the particulate material is ejected (whenimpacting is performed by ejecting the particulate material from anorifice), and the characteristics of the green body itself, includingthe porosity of the surface region of the green body (which derives fromthe ratio of metal powder to extractable material during the fabricationof the green body) and the pressure at which the metal powder and spaceholder particle mixture is compacted to form the green body.

The particulate material that is used for impacting the green body maybe soluble in an aqueous solvent, an organic solvent, or both. Theparticulate material may include a salt, a sugar, a solid hydrocarbon, aurea derivative, a polymer, or any combination thereof. Suitableexamples include sodium chloride, potassium chloride, sucrose, potassiumsorbate, carbamide, biuret, ammonium carbonate, ammonium bicarbonate,naphthalene, or any combination thereof. Additionally or alternatively,the particulate material may be removable under heat and/or pressureconditions; for example, the particulate material may volatilize, melt,or otherwise dissipate as a result of heating. Examples of suchparticulate materials include ammonium bicarbonate, urea, biuret,melamine, ammonium carbonate, naphthalene, sodium bicarbonate, and anycombination thereof. The thermal removal of particulate material may beconducted as a heating cycle that is independent from any sinteringstep, or may be part of a continuous furnace cycle that at immediatelyprecedes and “ramps up” to sintering. Preferably, the thermal removal ofparticulate material is performed at temperatures much lower thansintering temperature, in order to avoid contamination of the green bodymaterial with C, N, or H from organic space holders. For example, thethermal removal of particulate material may occur at less than about100° C., which is sufficient to cause the decomposition of someparticulate materials, such as ammonium bicarbonate.

The particulate material may comprise particles that are of irregular orvaried shapes and a mixture of sizes, or may comprise particles that areof substantially uniform sizes, shapes, or both. For example, theparticles of the particulate material may be substantially spherical,oblong, or may be crystalline and adopt any of a number of differentcrystal conformations. In one embodiment, the particulate materialcomprises particles having an average diameter (e.g., along the majordimension of any given particle) of about 150 μm to about 1250 μm.

The force with which the particulate material strikes the green body canaffect the displacement of metal powder from the green body. The “force”with which the particulate material strikes the green body may beexpressed in terms of pressure, for example, in units ofpound-force-per-square-inch. In accordance with the present invention,the particulate material may impact the green body at a pressure ofabout 3 psi to about 30 psi, for example at about 5 psi, about 7 psi,about 10 psi, about 15 psi, about 20 psi, about 25 psi, about 27 psi, orabout 30 psi. The amount of force/pressure with which the green body isimpacted with the particulate material may vary during the process ofimpacting; for example, the force/pressure with which the green body isimpacted may be increased over the course of the impacting process, maybe decreased, or may be alternately decreased and increased.

In addition, the amount of time during which the impacting is effectedcan affect the displacement of the metal powder from the green body. Incertain embodiments, the impacting is effected for no more than about 2seconds to about 2 minutes, preferably no more than about 2 seconds toabout 30 seconds. The impacting time may depend upon part size; the“stream” of particulate material may be wide enough to cover the entirefacing surface of certain small parts, whereas more time may be requiredif the part features more surface area. The impacting of the green bodywith the particulate material may be performed as a single episode,i.e., over a single, continuous period of time, or may occur as severalepisodes, for example, with one episode of impacting, followed by aperiod during which no impacting occurs, followed by a second episode ofimpacting, with this cycle optionally repeated one or more times. Eachepisode of impacting optionally is effected for no more than about 1second to about 2 minutes, preferably no more than about 1 second toabout 30 seconds.

The impacting of the green body with the particulate material may beaccomplished by ejecting the particulate material from a suitablestructure, such as an orifice that is connected to a source ofparticulate material. The particulate material may be ejected from anorifice that is positioned about 2 inches from about 30 inches from thegreen body during the impacting process. The orifice and the green bodymay be stationary with respect to one another, i.e., may be fixed suchthat the distance between them does not change during impacting.Alternatively, the impacting process may be carried out such that thedistance between the green body and the orifice increases, decreases, orboth during the impacting process.

The green body may be stationary during the impacting process, or may berotated, laterally shifted, or otherwise spatially translated in order,for example, to allow multiple surfaces of the green body to be impactedby the particulate material. The same result may be achieved by changingthe orientation of the source of the particulate material relative tothe green body. In one example, the green body may be rotated at a givenspeed, or the speed with which the green body is rotated may vary overthe course of the impacting process. The green body may be rotated atspeeds varying from about 5 rpm to about 100 rpm, preferably from about10 rpm to about 60 rpm, during impacting. In other embodiments thesource of the particulate material may be moved relative to a stationarygreen body, for example, at a rate of about 0.1 in/s, about 0.2 in/s,about 0.25 in/s, about 0.5 in/s, about 1.0 in/s, about 1.5 in/s, about2.0 in/s, about 2.5 in/s, about 3.0 in/s, about 3.5 in/s, about 4.0in/s, or greater.

During the impacting process, there is a tendency for the particulatematerial to lodge into the surface of the green body. When the greenbody has been prepared using the “space holder” method, i.e., compactinga mixture of metal powder and extractable material, followed optionallyby processing (such as machining), and by removal of at least a portionof the extractable material (either by treatment with solvent or byheating), it is also possible that some extractable material may remainwithin the green body. Accordingly, following the impacting process, thepresent methods may further comprise exposing the green body to asolvent in which the particulate material is soluble, in which theextractable material is soluble, or both. For example, if theparticulate material is soluble in an aqueous fluid, the green body maybe immersed in a bath comprising an aqueous fluid following theimpacting process. The exposure of the green body to an aqueous fluidwill remove all or substantially all of the particulate material fromthe impacting process, and may also serve to remove all or substantiallyall of any remaining extractable material. Alternatively, if theparticulate material is not soluble in an aqueous or organic fluid butis instead removable by heat, any particulate material that is embeddedin the green body can be removed via heating. Such heating may beaccomplished during the “ramp up” period pursuant to a sinteringprocess, which is traditionally performed with respect to a green bodyin order to prepare an implant.

Following the impacting process and, where necessary, the removal ofparticulate material and/or extractable material from the green body,the present methods may further comprise sintering the green body.Sintering is typically performed in a vacuum furnace and those skilledin the art will readily appreciate the appropriate conditions forsintering a green body comprising a metal powder. Sintering may befollowed by additional processing steps, including machining to refinethe shape characteristics of the sintered body.

An exemplary manufacturing process in accordance with the presentinvention is illustrated in FIG. 1. As described above, the process maybegin by mixing at least one metal powder with an extractable material,shaping the powder mixture into a shaped object, compacting the shapedobject to form a green body, and optional processing of the shapedobject (e.g., by machining), followed by processing the green body,removal of the extractable material (such as by exposing the green bodyto a solvent in which the extractable material is soluble), impactingthe green body with a particulate material, optionally removing theparticulate material from the green body (for example, by exposing thegreen body to a solvent in which the particulate material is soluble),sintering the green body, and, if desired, final processing (e.g., bymachining) in order to form an implant. In view of the precedingdiscussion, it will be apparent that various of the illustratedprocessing steps can be modified or altered, or in some cases entirelyomitted, according to the needs of the manufacturer and/or the desiredproduct. The schematic illustrated in FIG. 1 is but one embodiment andis intended to depict but one possible processing route in accordancewith the present invention.

The present methods may further comprise surgically installing animplant made in accordance with the above-described impacting andsintering steps. An implant that is made in accordance with the recitedimpacting and sintering steps will possess characteristics that, asdescribed above, are particularly well suited for ensuring stabilityupon surgical implantation, favorable biological fixation, andintegration in situ with bone and tissue via ingrowth.

In accordance with the present invention there are also providedimplants comprising a metallic matrix. One or more surfaces of thepresent implants may possess specific characteristics (e.g., staticfriction coefficient, various aspects of surface geometry), that aredistinguishable from those that are present with respect to the surfacesof traditional implants. In one embodiment, at least one surface of themetallic matrix has a static friction coefficient of about 0.7 or higherwith a polymer bone analog comprising polyurethane foam having a densityof about 20 lb/ft³. Implants comprising a metallic matrix that arecoated on a surface with a porous coating product may yield a staticfriction coefficient of about 0.7 or higher with a polymer bone analog,but the static friction coefficient is attributable to the coating, notto the surface of the metallic matrix itself. In addition, the roughnessof conventional porous coated products usually derives from the shape ofthe metal powders, wires, or fibers used to form the coating and theirarrangement on the surface of the part, which is highly dependent uponhow the coating is deposited on the substrate. In other embodiments ofthe present invention, at least one surface of the metallic matrix has astatic friction coefficient of about 0.7 to about 1.5 with a polymerbone analog. Thus, the present implants provide a high static frictioncoefficient at one or more surfaces of the metallic matrix, unlike animplant that is coated at one or more surfaces with a porous coatingproduct. The polymer bone analog comprising polyurethane provides areference point with respect to the inventive implants. To the extentthat the characteristics of the instant implants can be described byreference to a different friction substrate, the scope of instantinvention should not be construed as being limited to implants that canonly be described by reference to a polymer bone analog comprisingpolyurethane foam having a density of about 20 lb/ft³. One example ofthe recited bone analog is Cat. No. FR-4520 from General PlasticsManufacturing Co. (Tacoma, Wash.), which is said to be a “rigid,closed-cell polyurethane foam” with a density of 20 lb/ft³.

Also disclosed are implants or other articles of manufacture at least aportion of which comprises metallic matrix, wherein at least a secondportion of which comprises a substrate material, which may be a solidsubstrate. For example, the implant or article of manufacture maycomprise a layer or coating of metallic matrix material having athickness of about 0.5 mm to about 50 mm, on at least a portion of asolid substrate. In such embodiments, one or more surfaces of themetallic matrix may possess specific characteristics (e.g., staticfriction coefficient, various aspects of surface geometry/roughness),that are distinguishable from those that are present with respect to thesurfaces of traditional implants. Throughout the present disclosure, an“implant comprising a metallic matrix” may refer to an implant orarticle of manufacture that comprises a coating of metallic matrixmaterial on at least a portion of a solid substrate.

The metallic matrix of the present implants and coatings may comprisetitanium, a titanium alloy, a cobalt-chromium alloy, molybdenum,tantalum, niobium, zirconium, stainless steel, or any combinationthereof.

Also provided are implants comprising a metallic matrix, wherein atleast one surface of the metallic matrix has a roughness thatcorresponds to a Pa value of at least about 20, a roughness thatcorresponds to a Pp value of at least about 60, a roughness thatcorresponds to a Pt value of at least about 140, or a roughness thatcorresponds to a Pq value of at least about 30. The Pa parameterrepresents the arithmetic average value of the unfiltered raw profiledeparture from the mean line within a sampling length; Pp is the largestpeak deviation of the unfiltered raw roughness profile from the meanline within a sampling length; Pt is the maximum peak to valley heightof the unfiltered raw profile in the evaluation length; and Pq is thesquare root of the mean of all the ‘z’ values after they have beensquared, defined over one sampling length. These parameters are pursuantto ISO 4287 (1997). In other embodiments the disclosed implants comprisea metallic matrix, wherein at least one surface of the metallic matrixhas a roughness that corresponds to a Pa value of at least about 50, aroughness that corresponds to a Pp value of at least about 90, aroughness that corresponds to a Pt value of at least about 200, or aroughness that corresponds to a Pq value of at least about 60. In yetother embodiments of the present implants, at least one surface of themetallic matrix has a roughness that corresponds to a Pa value of atleast about 70, a roughness that corresponds to a Pp value of at leastabout 120, a roughness that corresponds to a Pt value of at least about300, or a roughness that corresponds to a Pq value of at least about 70.

Also provided are methods comprising surgically installing an implantcomprising a metallic matrix, wherein at least one surface of themetallic matrix has a static friction coefficient of about 0.7 or higherwith a polymer bone analog comprising polyurethane foam having a densityof about 20 lb/ft³. In another aspect, provided are methods comprisingsurgically installing an implant comprising a metallic matrix, whereinat least one surface of the metallic matrix has a static frictioncoefficient of about 0.7 to about 1.5 with a polymer bone analog. Inother embodiments there are provided methods comprising surgicallyinstalling an implant comprising a metallic matrix, wherein at least onesurface of the metallic matrix has a roughness that corresponds to a Pavalue of at least about 20, a roughness that corresponds to a Pp valueof at least about 60, a roughness that corresponds to a Pt value of atleast about 140, or a roughness that corresponds to a Pq value of atleast about 30. The implant comprising a metallic matrix may have atleast one surface that has a roughness that corresponds to a Pa value ofat least about 50, a roughness that corresponds to a Pp value of atleast about 90, a roughness that corresponds to a Pt value of at leastabout 200, or a roughness that corresponds to a Pq value of at leastabout 60. In yet other embodiments, at least one surface of the metallicmatrix that is surgically installed in accordance with the presentmethods has a roughness that corresponds to a Pa value of at least about70, a roughness that corresponds to a Pp value of at least about 120, aroughness that corresponds to a Pt value of at least about 300, or aroughness that corresponds to a Pq value of at least about 70. Themetallic matrix of the implant that is surgically installed pursuant tothe present methods may comprise titanium, a titanium alloy, acobalt-chromium alloy, molybdenum, tantalum, niobium, zirconium,stainless steel, or any combination thereof.

EXAMPLES Example 1 Topography of Green Body Impacted with ParticulateMaterial

FIGS. 2A and 2B each depict a lateral view of a cross section throughthe surface of a green body of which certain sections have been impactedwith a particulate material for a time and under conditions effective todisplace a portion of the metal powder from the green body. Forcomparative purposes, sections near the ends of each green body (markedby brackets) were not processed in accordance with the presentinvention, i.e., were not impacted with the particulate material. Thesurface characteristics of the unprocessed sections are easilydistinguishable from those of the sections of the green body that wereimpacted with the particulate material. In each image, the whitematerial is the metal matrix, and black represents pores or empty space.The green body in FIG. 2A comprises compacted metal powder ofCommercially Pure (“CP”) Ti and was impacted with a particulate materialcomprising sodium chloride, ejected at a pressure of 15 psi from anorifice located about 6 inches from the green body for about 2 seconds.The green body in FIG. 2B comprises compacted metal powder of CP Ti andwas impacted with a particulate material comprising sodium chloride,ejected at a force of 25 psi from an orifice located about 12 inchesfrom the green body for 2 seconds. The conditions under which the greenbody in FIG. 2B was impacted with the particulate material resulted inmore significant displacement of metal powder from the surface of thegreen body, thereby yielding larger and deeper pits, and by extension,higher peaks.

Example 2 Variation of Parameters of Impacting Process

Table 1, below, depicts three exemplary embodiments in which parametersof the impacting process were varied:

TABLE 1 Green Body Type Impacting Working Trans- of Green ParticulatePressure Distance Time lation Body Material (psi) (in) (sec) (rpm)Rabbit distal <250 μm NaCl 5 3 4 15 femur implant (NaCl particles(cylindrical) smaller than 250 μm in largest dimension) 58 mm <250 μmNaCl 20 7 10 50 diameter acetabular cup 1 in² friction <250 μm NaCl 2012 3 none coupon (rectangular prism) 1.25 inch <250 μm NaCl 10 2 2 nonediameter coupon 1.25 inch <250 μm NaCl 10 4 2 none diameter coupon 1.25inch <250 μm NaCl 15 2 2 none diameter coupon 1.25 inch <250 μm NaCl 154 2 none diameter couponFavorable results were obtained with respect to each of the green bodiesthat were subjected to an impacting process under the respectiveconditions described in Table 1; each of the green bodies featuredroughened surfaces as compared with untreated green bodies.

Example 3 Measurement of Static Friction Coefficient

Static friction coefficient was measured as between each of threedifferent materials (each of materials A-C, as shown in FIG. 3) and abone analogue, specifically Cat. No. FR-4520 from General PlasticsManufacturing Co. (Tacoma, Wash.), said to be a “rigid, closed-cellpolyurethane foam” with a density of 20 lb/ft3. The first material (A)was a sintered, CP Ti foam structure of roughly 75% volume porosity thatwas prepared in accordance with the conventional “space holder”technique. The surface tested on this sample was machined flat while thesample was in the green state. The second material (B) was a sintered CPTi foam structure of roughly 75% volume porosity. The surface tested onthis samples was also machined flat while the sample was in the greenstate, but the surface was then also impacted with NaCl according to theconditions listed in Table 1; the test surface of the second materialwas therefore prepared in accordance with an embodiment of the presentinvention. The third material (C) consisted of POROCOAT® beaded porouscoating (DePuy Orthopaedics, Inc., Warsaw, Ind.), a sintered coating ofspherical unalloyed titanium beads on a Ti-6Al-4V susbtrate.

As shown in FIG. 3, material B had a static friction coefficient withthe bone analogue that was comparable with that of material C, andstatistically higher than the static friction coefficient measured withrespect to material A, which is a metallic matrix that were prepared inaccordance with the conventional “space holder” approach.

Example 4 Additional Measurements of Static Friction CoefficientInvolving Exemplary Embodiments

Static friction coefficient was measured for 0.75 in×0.75 squaremetallic matrix samples prepared from CP Ti or Ti-6Al-4V under 30 or 45ksi cold isostatic compaction and otherwise in accordance with theconventional “space holder” technique, and having a porosity of about73% or about 75% after sintering. The samples were either subjected toimpaction by NaCl particles (Morton's Popcorn Salt®) of which at least95% by weight were smaller than 250 μm, or were machined in the greenstate without being subjected to impaction with a particulate material.For the samples that were subjected to impaction, the particulatematerial comprising sodium chloride was ejected at a force of 5 psi, 10psi, 15, psi, 20 psi, or 25 psi from an orifice located about 4 to 8inches from the green body; two passes of the “blast” stream, with theblasting apparatus moving at about 1 inch/s, were performed with respectto each sample.

The friction test was performed using a “sled on a plane” method. The“sled” consisted of the 0.75 in×0.75 square metallic matrix samples,whereas each “plane” was a milled sample of Last-A-Foam® 6720 (GeneralPlastics Manufacturing Company, Tacoma, Wash.), a rigid, closed-cellpolyurethane foam with a density of 20 lb/ft³. Each sled was connectedto a 250 N load cell by 10 lb monofilament line and pulled at 10 mm/minfor 0.8 in. A weight was placed on the sled to create a normal force of30 N. The static friction coefficient was calculated from the maximumforce recorded before the first 0.5 N drop in force. Each sample wassubjected to three separate test runs, and was ultrasonically cleaned inacetone between tests. The results are depicted in Tables 2 and 3,below:

TABLE 2 74% Porosity/45 ksi 73% Porosity/45 ksi 73% Porosity/ Blastingcompaction compaction 30 ksi Pressure CP Ti Ti64 CP Ti Ti64 CP Ti (psi)Avg Std Dev Avg Std Dev Avg Std Dev Avg Std Dev Avg Std Dev As- 0.52 0.10.65 0.01 Machined  5 0.83 0.06 10 0.72 0.14 1.09 0.21 0.97 0.11 15 0.890.18 1.35 0.09 0.69 0.06 1.02 0.07 0.87 0.07 20 0.87 0.09 0.96 0.07

TABLE 3 Blasting 75% Porosity/45 ksi compaction Pressure CP Ti Ti64(psi) Avg Std Dev Max Min Avg Std Dev Max Min As- 0.52 0.1 n = 1 0.650.01 n = 1 Machined 5 10 0.72 0.14 0.74 0.67 1.09 0.21 1.30 0.99 15 0.890.18 0.98 0.82 1.35 0.17 1.51 1.10 20Static friction coefficient ranged from about 0.7 to about 1.5, andincluded values of, inter alia, about 0.5, about 0.6, about 0.7, about0.8, about 0.9, about 1.0, about 1.1, about 1.2, about 1.3, about 1.4,and about 1.5.

Example 5 Correlation Between Pressure Used During Impacting(“Blasting”) Process and Surface Roughness

FIGS. 4-10 depict graphs that compare average surface roughness valuesobtained from metallic matrix samples with the pressure (psi) at whichthe corresponding green body sample from which the metallic matrixsamples were prepared was impacted (“blasted”) with the particulatematerial. The graphs are labeled to indicate the material from which themetallic matrix was prepared (CP Ti or Ti-6Al-4V) and the porosity ofthe sample (73% or 75%). Surface roughness was assessed using a ZeissSurfcomm 5000 (Carl Zeiss Inc., Germany) contact profilometer fittedwith a 500 μm radius ruby ball as the stylus. Ten parallel 14-mm longtraces were acquired from each sample, spaced about 1.5 mm apart toobtain measurements of the unfiltered P profile with a measurement speedof 0.3 mm/sec and a “least square straight” tilt correction, a. Pa(FIGS. 4 and 8) represents the arithmetic average value of theunfiltered raw profile departure from the mean line within a samplinglength; Pp (FIGS. 5 and 9) is the largest peak deviation of theunfiltered raw roughness profile from the mean line within a samplinglength; Pt (FIGS. 6 and 10) is the maximum peak to valley height of theunfiltered raw profile in the evaluation length; and Pq (FIG. 7) is thesquare root of the mean of all the ‘z’ values after they have beensquared, defined over one sampling length. These parameters are pursuantto ISO 4287 (1997). In FIGS. 4-10, diamonds (♦) represent samples havingsurfaces that were subjected to impaction with particulate materialwhile in the green state in accordance with the presently disclosedtechniques, whereas the squares (▪) represent samples that were machinedin the green state and not subjected to the impacting procedure.

Table 3, below, provides the compiled average surface roughnessmeasurements for CP-Ti metallic matrices having a porosity of about 73%that were prepared from green bodies that were impacted with aparticulate material in accordance with the presently disclosedtechniques. Surface roughness is expressed in terms of the Pa, Pp, Pt,and Pq parameters, respectively, as defined above.

TABLE 3 Blasting Pressure (ksi) Pa Pp Pt Pq CP-Ti 0 18.6 49.0 129.2 24.510 52.9 126.5 360.6 66.9 15 58.4 126.8 367.7 73.3 20 58.1 124.3 351.271.9 25 86.6 188.4 509.7 107.0

Table 4, below, provides the compiled average surface roughnessmeasurements for Ti-64 metallic matrices having a porosity of about 75%that were prepared from green bodies that were impacted with aparticulate material in accordance with the presently disclosedtechniques, or sintered in the as-machined state (i.e., were notimpacted with particulate material while in the green state). Surfaceroughness is expressed in terms of the Pa, Pp, Pt, and Pq parameters,respectively, as defined above.

TABLE 4 Blasting Pressure (ksi) Pa Pp Pt Pq Ti-64 0 12.7 37.1 85.6 15.810 78.6 178.8 444.2 96.6 15 181.4 402.8 816.7 212.8 20 25

Table 5, below, provides the average surface roughness measurements forCP-Ti metallic matrices having a porosity of either about 73% or about75% (as labeled) that were prepared from green bodies that were eitherimpacted with a particulate material in accordance with the presentlydisclosed techniques, or sintered in the as-machined state (i.e., werenot impacted with particulate material while in the green state).Surface roughness is expressed in terms of the Pa, Pp, Pt, and Pqparameters, respectively, as defined above.

TABLE 5 Blasting Pressure Sample Name (ksi) Pa Pp Pt Pq 73% 15-4-1 1534.5 63 226.9 44.9 porous 15-6-1 15 45.8 91.6 303.6 59.1 CP Ti 15-8-1 1531.3 61.6 257.3 42.2 20-4-1 20 48.0 97.7 288.4 59.1 20-6-1 20 61.7 144408.6 78.3 20-8-1 20 57.5 113 327.9 70.1 20-6-2 20 65.3 141 379.9 80.225-6-2 25 86.6 188 509.7 107.0 as-machined 0 13.8 37.8 94.1 17.3 73% 75%as-machined 0 18.6 49.0 129.2 24.5 porous 75% CP Ti

Table 6, below, provides the average surface roughness measurements forTi-6Al-4V metallic matrices having a porosity of either about 73% orabout 75% (as labeled) that were prepared from green bodies that wereeither impacted with a particulate material in accordance with thepresently disclosed techniques, or sintered in the as-machined state(i.e., were not impacted with particulate material while in the greenstate). Surface roughness is expressed in terms of the Pa, Pp, Pt, andPq parameters, respectively, as defined above.

TABLE 6 Blasting Sample Pressure Name (ksi) Pa Pp Pt Pq 75% b-3 10 83.2186.8 491.1 103.0 porous a-3 10 74.0 170.7 397.2 90.2 Ti—6Al—4V c-4 15181.4 402.8 816.7 212.8 As- 0 12.7 37.1 85.6 15.8 machined 75% Ti—6Al—4V

While the invention has been described and illustrated with reference tospecific embodiments, those skilled in the art will recognize thatmodifications and variations may be made without departing from theprinciples of the invention as described herein and set forth in thefollowing claims.

1. A method for processing a green body that includes compacted metalpowder, comprising impacting said green body with a particulate materialfor a time and under conditions effective to displace a portion of saidmetal powder from said green body.
 2. The method according to claim 1further comprising sintering said green body.
 3. A method comprisingsurgically installing an implant made in accordance with the method ofclaim 2 into a patient.
 4. The method according to claim 1 furthercomprising: mixing at least one metal powder with an extractablematerial, thereby forming a powder mixture in which said metal powderand extractable material assume respective positions; shaping saidpowder mixture into a shaped object; and, compacting said shaped objectto form said green body.
 5. The method according to claim 4 furthercomprising processing said green body.
 6. The method according to claim4 wherein said powder mixture comprises about 18 wt. % to about 67 wt. %metal powder, the balance of said powder mixture comprising saidextractable material.
 7. The method according to claim 4 furthercomprising exposing said green body to a solvent in which saidextractable material is soluble.
 8. The method according to claim 7wherein said extractable material is soluble in an aqueous solvent, anorganic solvent, or both.
 9. The method according to claim 7 whereinsaid green body is immersed in said solvent.
 10. The method according toclaim 4 further comprising heating said green body for a time and underconditions effective to evaporate at least some of said extractablematerial yet substantially maintain said metal powder in its position insaid green body.
 11. The method according to claim 1 wherein said greenbody further includes an extractable material.
 12. The method accordingto claim 1 wherein said metal powder comprises titanium, a titaniumalloy, a cobalt-chromium alloy, molybdenum, tantalum, niobium,zirconium, stainless steel, or any combination thereof.
 13. The methodaccording to claim 1 wherein said particulate material is removable byheating.
 14. The method according to claim 13 wherein said particulatematerial comprises ammonium bicarbonate, urea, biuret, melamine,ammonium carbonate, naphthalene, sodium bicarbonate, or any combinationthereof.
 15. The method according to claim 1 wherein said particulatematerial is soluble in an aqueous fluid, and said method furthercomprises immersing said green body in a bath comprising an aqueousfluid prior to sintering said green body.
 16. The method according toclaim 15 wherein said particulate material comprises a salt.
 17. Themethod according to claim 1 wherein the green body has a porosity ofabout 50% to about 90%.
 18. The method according to claim 1 wherein saidparticulate material comprises particles having an average diameter ofabout 150 μm to about 1250 μm.
 19. The method according to claim 1wherein said particulate material impacts said green body with apressure of about 3 psi to about 25 psi.
 20. The method according toclaim 1 wherein impacting is effected for no more than about 2 secondsto about 30 seconds.
 21. The method according to claim 1 wherein saidparticulate material is ejected from an orifice that is positioned about2 inches to about 30 inches from said green body.
 22. A green bodyprepared according to the method of claim
 1. 23. An implant comprising ametallic matrix, wherein at least one surface of the metallic matrix hasa static friction coefficient of at least about 0.7 with a polymer boneanalog comprising polyurethane foam having a density of about 20 lb/ft³.24. The implant according to claim 23 wherein said metallic matrixcomprises titanium, a titanium alloy, a cobalt-chromium alloy,molybdenum, tantalum, niobium, zirconium, stainless steel, or anycombination thereof.
 25. The implant according to claim 23 wherein atleast one surface of the metallic matrix has a static frictioncoefficient of about 0.7 to about 1.5 with said polymer bone analog. 26.A method comprising surgically installing an implant according to claim23 into a patient.
 27. An implant comprising a metallic matrix, whereinat least one surface of the metallic matrix has a roughness thatcorresponds to a Pa value of at least about 20, a roughness thatcorresponds to a Pp value of at least about 60, a roughness thatcorresponds to a Pt value of at least about 140, or a roughness thatcorresponds to a Pq value of at least about
 30. 28. The implantaccording to claim 27, wherein at least one surface of the metallicmatrix has a roughness that corresponds to a Pa value of at least about50, a roughness that corresponds to a Pp value of at least about 90, aroughness that corresponds to a Pt value of at least about 200, or aroughness that corresponds to a Pq value of at least about
 60. 29. Theimplant according to claim 27, wherein at least one surface of themetallic matrix has a roughness that corresponds to a Pa value of atleast about 70, a roughness that corresponds to a Pp value of at leastabout 120, a roughness that corresponds to a Pt value of at least about300, or a roughness that corresponds to a Pq value of at least about 70.30. A method comprising surgically installing an implant according toclaim 27 into a patient.